As the exhaust gas purification system that purifies and exhausts the exhaust gas from the diesel engine, there has been developed an exhaust gas purification system in which DPD and SCR (Selective Catalytic Reduction) devices are connected to an exhaust pipe.
In this exhaust gas purification system, the DPD traps the PM contained in the exhaust gas. Moreover, in the exhaust gas purification system, an SCR system including the SCR device supplies an aqueous urea solution stored in a urea tank to the upstream of the exhaust gas in the SCR to generate ammonia by the heat of the exhaust gas. NOx is reduced by the ammonia on an SCR catalyst and purified (refer to Patent Documents 1 and 2, for example).
The PM trapped and accumulated in the DPD needs to be oxidized and removed to regenerate the DPD as appropriate in order to prevent clogging in a filter.
The clogging is detected by an exhaust pressure sensor that detects the differential pressure between the front and the back of the DPD. When the differential pressure has reached the upper limit, an ECU (Engine Control Unit) starts regenerating the DPD either automatically or manually. In the manual regeneration, the DPD starts regenerating once the ECU has turned on a DPD alarm lamp provided in a cabin and a driver has pressed a regeneration execution switch.
The DPD is regenerated by performing multi-injection of a fuel (pilot injection, pre-injection, main injection, and after-injection) to raise the exhaust temperature equal to or higher than a catalyst activation temperature of the DPD, followed by post-injection in addition to the multi-injection to raise the exhaust temperature up to approximately 600° C., thereby combusting and removing the PM trapped in the DPD by the high-temperature exhaust gas.
The DPD is regenerated automatically while a vehicle is in motion. Hence, the drive performance is determined by a full-load injection quantity of the fuel that is set intentionally low in a normal drive mode in consideration of a fuel quantity to be injected by the post-injection at the time of regeneration.
Now, when the vehicle travels in an upland area, i.e., at high altitudes of 2000 m and 3000 m where the air (oxygen) is thin, the atmospheric pressure is reduced to approximately 80 kPa (at 2000 m) and approximately 70 kPa (at 3000 m) as compared to approximately 100 kPa at an altitude of 0 m, thereby requiring engine performance at full load to be degraded.